Dual-exporting .NET metrics with OTLP and Prometheus

To facilitate a low-risk migration from Prometheus to OpenTelemetry, .NET applications can use the `Meter` class to dual-export metrics to both systems simultaneously. This incremental approach allows developers to maintain Prometheus scraping while also pushing metrics via OTLP to an OpenTelemetry-compatible backend, enabling side-by-side comparison to ensure data consistency.